Is GSM a blackbox in OpenMoko

Henryk Plötz henryk at
Sat Dec 15 04:53:35 CET 2007


Am Fri, 14 Dec 2007 16:04:35 +0100 schrieb Torsten Schlabach:

>  > It is called Certification or Approval.
> I see. In Germany AFAIK this is the Bundesnetzagentur, formerly known
> as RegPT (Regulierungsbehörde für Post und Telekommunikation, just
> for the non Germans on this list). And I know that each country has a
> similar authority, which is in charge or regulating and licensing the
> use of radio spectrum as well as making sure that devices which use
> radio frequencies do not cause other users any trouble, etc.

Yes, and also look to the fact that GSM is an incredibly brittle
protocol which is only still working because not everybody can fool
around with their handset's innards. You know those guys who would go
to great lengths for 'boosting' their Wifi AP's signal even though
doing so accomplishes nothing but blurting trash into neighbouring
GSM is even worse. For example there are flag bits in there indicating
that you're an emergency worker and need access to the net even when
the general public is barred (e.g. in states of emergency). I guess
it's also very likely that you could bring down fairly large areas of
coverage by blurting out the wrong bits over the air (fuzzing anyone?).
For more hands-on work I'd recommend

>  > And since the SIM card plays a crucial role in that, it is  simply
>  > not possible to access the SIM card directly by software. No
>  > manufacturer in this world can change that.
> I doubt this is acurate. 

Right, there are even AT commands for limited SIM access through the
modem (AT+CSIM and AT+CRSM), though expectedly you can't do anything
fun with them.

Now on to your point: With the Neo1973 you can at least have some part
of your wish: You get all the information needed to do hardware
modifications. While it's true that the SIM card slot in the Neo is
connected directly to the modem that doesn't mean you can't do
something with it. In principle it should be possible to connect the
SIM slot back to the CPU, e.g. by using a SIM sized adaptor (like
bottom right) and some spare I/O lines (look into the Wiki if there's
anything, or ask around, ask roh if you can't find anything).

You should be able to mostly emulate/relay a SIM card in software with
this method. Why you would want to do that is of course a different

> One hot application these days is dual-SIM phones. Many people have 
> several SIM cards these days to use in different networks for various 
> reasons, but there's nothing wrong with that I think. But people
> don't necessary want to carry 2,3 or more phones.

IIRC you'd need dual radios for that anyways.

Henryk Plötz
Grüße aus Berlin
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